WO2015190265A1 - 電池用セパレータ及びその製造方法 - Google Patents
電池用セパレータ及びその製造方法 Download PDFInfo
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- WO2015190265A1 WO2015190265A1 PCT/JP2015/064696 JP2015064696W WO2015190265A1 WO 2015190265 A1 WO2015190265 A1 WO 2015190265A1 JP 2015064696 W JP2015064696 W JP 2015064696W WO 2015190265 A1 WO2015190265 A1 WO 2015190265A1
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- laminated
- polyolefin
- microporous membrane
- battery separator
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
- H01M50/406—Moulding; Embossing; Cutting
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/431—Inorganic material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/443—Particulate material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/463—Separators, membranes or diaphragms characterised by their shape
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/494—Tensile strength
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to a battery separator having at least a laminated polyolefin microporous membrane suitable for laminating a modified porous layer and a modified porous layer. It is a battery separator useful as a lithium ion battery separator.
- Thermoplastic resin microporous membranes are widely used as separators and filters.
- separators for lithium ion secondary batteries nickel-hydrogen batteries, nickel-cadmium batteries, polymer batteries, separators for electric double layer capacitors, and reverse osmosis filtration membranes, ultrafiltration membranes for filters And microfiltration membranes.
- it is used for moisture permeable waterproof clothing, medical materials, and the like.
- a separator for a lithium ion secondary battery it has ion permeability when impregnated with an electrolytic solution, is excellent in electrical insulation, electrolytic solution resistance, and oxidation resistance, and has a temperature of about 120 to 150 ° C. when the battery is abnormally heated.
- a microporous polyethylene membrane having a pore closing effect that blocks ion permeability and suppresses excessive temperature rise is preferably used.
- a film breakage may occur due to a decrease in the viscosity of the polyethylene constituting the film or a contraction of the film. This phenomenon is not limited to polyethylene, and even when other thermoplastic resins are used, the phenomenon cannot be avoided beyond the melting point of the resin constituting the microporous film.
- Lithium-ion battery separators are related to battery characteristics, battery productivity, and battery safety, and include mechanical characteristics, heat resistance, permeability, dimensional stability, pore plugging characteristics (shutdown characteristics), and melt-breaking characteristics (meltdown). Characteristics) and the like are required. Furthermore, in order to improve the cycle characteristics of the battery, it is required to improve the adhesion with the electrode material and to improve the electrolyte permeability to improve the productivity.
- modified porous layer a polyamide-imide resin, a polyimide resin, a polyamide resin and / or a fluorine-based resin excellent in electrode adhesion, which have both heat resistance and electrolyte solution permeability are preferably used.
- a water-soluble or water-dispersible binder capable of laminating a modified porous layer using a relatively simple washing step and drying step is also widely used.
- the modified porous layer in the present invention refers to a layer containing a resin that imparts or improves at least one function such as heat resistance, adhesion to an electrode material, and electrolyte permeability.
- the battery separator needs to increase the area that can be filled in the container in order to improve the battery capacity, and it is predicted that the thinning will proceed.
- the microporous membrane is likely to be deformed in the planar direction as the thickness of the microporous membrane is reduced, the battery separator in which the modified porous layer is laminated on the microporous membrane is being processed, in the slit process or the battery assembly process.
- the modified porous layer may peel off, making it more difficult to ensure safety.
- Patent Document 1 polyvinylidene fluoride is applied to a polyethylene microporous film having a thickness of 9 ⁇ m, and a part of the polyvinylidene fluoride bites into the pores of the polyethylene porous film appropriately so as to express an anchor effect.
- a composite microporous membrane having a peel strength (T-type peel strength) at the interface between the porous membrane and the polyvinylidene fluoride coating layer of 1.0 to 5.3 N / 25 mm is disclosed.
- Patent Document 2 a heat-resistant porous layer containing a self-crosslinkable acrylic resin and plate-like boehmite is provided on a corona discharge-treated polyethylene microporous film having a thickness of 16 ⁇ m, and a polyethylene microporous film and a heat-resistant porous layer are provided.
- a separator having a peel strength at 180 ° (T-type peel strength) of 1.1 to 3.0 N / 10 mm is disclosed.
- Example 1 of Patent Document 3 47.5 parts by mass of polyethylene having a viscosity average molecular weight of 200,000, 2.5 parts by mass of polypropylene having a viscosity average molecular weight of 400,000, 50 parts by mass of a composition comprising an antioxidant, and 50 liquid paraffins.
- a polyethylene resin solution consisting of parts by mass is extruded from an extruder at 200 ° C., and a gel-like molded product is obtained while being drawn with a cooling roll adjusted to 25 ° C., and then biaxially stretched so as to be 7 ⁇ 6.4 times.
- a laminated microporous membrane obtained by laminating a coating layer made of polyvinyl alcohol and alumina particles on the surface of the polyethylene resin microporous membrane is disclosed.
- Example 6 of Patent Document 4 a polyethylene resin solution having a weight average molecular weight of 41.5 million, a weight average molecular weight of 560,000, a polyethylene composition of 30% by weight and a mixed solvent of liquid paraffin and decalin of 70% by weight is extruded. Extruded from the machine at 148 ° C., cooled in a water bath to obtain a gel-like molded article, and then biaxially stretched to a 5.5 ⁇ 11.0 times to obtain a polyethylene microporous film. A separator for a non-aqueous secondary battery obtained by laminating a coating layer made of meta-type wholly aromatic polyamide and alumina particles on the surface of this polyethylene microporous membrane is disclosed.
- Example 1 of Patent Document 5 47 parts by mass of homopolymer polyethylene having a viscosity average molecular weight of 700,000, 46 parts by mass of homopolymer polyethylene having a viscosity average molecular weight of 250,000, and 7 parts by mass of homopolymer polypropylene having a viscosity average molecular weight of 400,000 Were dry blended using a tumbler blender.
- Patent Document 6 discloses a separator for a lithium ion secondary battery in which a ceramic layer is laminated on a porous resin base material having a porous polyethylene layer as an inner layer and a porous polypropylene layer as an outer layer.
- Patent Document 7 discloses a technique for producing a microporous film by stretching a laminate having a layer to which a low-melting-point resin is added and a layer not containing the layer.
- Patent Document 8 discloses a separator for a non-aqueous electrolyte battery in which heat resistance at high temperature is improved by laminating an inorganic filler-containing layer on a polyolefin microporous film slightly containing polypropylene.
- JP 2012-037662 A Republished 2010-104127 Japanese Patent No. 4931083 Japanese Patent No. 4460028 JP 2011-000832 A JP 2011-071009 A Special table 2012-521914 gazette Japanese Patent No. 4789274
- the present invention assumes the case where the battery separator is made thinner and faster in the future, and the peel strength between the modified porous layer and the laminated polyolefin microporous film is high.
- An object of the present invention is to provide a battery separator suitable for high-speed processing, in which a modified porous layer is laminated on a polyolefin microporous membrane.
- FIG. 1 schematically shows the state of the side surface of a laminated sample of a laminated polyolefin microporous membrane and a modified porous layer in a state of being pulled by a tensile tester (not shown).
- 1 is a laminated sample
- 2 is a laminated polyolefin microporous membrane
- 3 is a modified porous layer
- 4 is a double-sided pressure-sensitive adhesive tape
- 5 and 5 'are aluminum plates and the arrows in the figure are tensile directions.
- the aluminum plate (5) and the aluminum plate (5 ′) are pulled in parallel in opposite directions using a tensile tester at a tensile rate of 10 mm / min, and the strength when the modified porous layer is peeled is measured.
- the peel strength is 130 N / 15 mm or more in this evaluation method, the laminated modified porous layer is being transported or processed even if the thickness of the laminated polyolefin microporous film is, for example, 10 ⁇ m or less. There is almost no peeling phenomenon.
- the T-type peel strength or 180 ° peel strength conventionally used as a peel strength measurement method is the peel force when the coating layer is peeled from the surface of the battery separator vertically or obliquely backward. is there. According to this evaluation method, it is possible to evaluate the abrasion resistance in the slit process and the battery assembly process more practically as compared with these conventional evaluation methods.
- the battery separator of the present invention has the following configuration. That is, A battery separator having a laminated polyolefin microporous membrane and a modified porous layer present on at least one surface thereof, wherein the laminated polyolefin microporous membrane comprises at least a layer A and a B layer.
- the laminate has a meltdown temperature of 165 ° C. or higher, an air resistance of 300 sec / 100 cc Air or less, and at least one surface facing the outside is 3 / cm 2 or more and 200 / cm 2 or less.
- Protrusions made of polyolefin are irregularly present, and the protrusions satisfy 0.5 ⁇ m ⁇ H (H is the height of the protrusions) and 5 ⁇ m ⁇ W ⁇ 50 ⁇ m (W is the size of the protrusions).
- battery separator comprising a can the be stacked on a surface having a projection of the laminated polyolefin microporous membrane, and a tensile strength of 5N / mm 2 or more binders and inorganic particles A.
- the surface facing the outside world means that at least one of the surfaces of each layer constituting the laminated polyolefin microporous membrane faces the side (interface side) in contact with the surface of the other layer, but on the interface side.
- the laminated polyolefin microporous membrane preferably has a three-layer structure of A layer / B layer / A layer or B layer / A layer / B layer, and the B layer has a heat of fusion of 90 J / g or more. More preferably, it comprises polypropylene which is In the battery separator of the present invention, the thickness of the B layer is preferably 3 ⁇ m or more and 15 ⁇ m or less.
- the binder preferably contains polyvinyl alcohol or an acrylic resin.
- the inorganic particles preferably contain at least one selected from the group consisting of calcium carbonate, alumina, titania, barium sulfate and boehmite.
- the battery separator manufacturing method of the present invention has the following configuration.
- Step of adding a molding solvent to the polyolefin resin constituting the A layer and then melt-kneading to prepare the polyolefin resin solution A (b) Molding into a polyolefin resin containing the polyethylene resin and polypropylene resin constituting the B layer
- Extruding the polyolefin resin solutions A and B obtained in steps (a) and (b) from a die at least one of them Is cooled with a cooling roll having a surface from which the forming solvent has been removed by the forming solvent removing means to form a laminated gel-like molded product
- the forming solvent removing means in the step (c) is preferably a means for scraping off using a doctor blade.
- a separator for a battery in which the modified porous layer is laminated on the laminated polyolefin microporous membrane having excellent adhesion to the modified porous layer does not cause peeling of the modified porous layer even during high-speed conveyance. Is obtained.
- the laminated polyolefin microporous membrane used in the present invention is suitable for the surface by adjusting the specific polyolefin resin solution and highly controlling the cooling rate of the polyolefin resin solution extruded from the extruder through the die. It has shape and number of protrusions.
- the present invention when a modified porous layer containing inorganic particles and a binder having a tensile strength of 5 N / mm 2 or more is laminated on a laminated polyolefin microporous membrane, the present invention is provided between the laminated polyolefin microporous membrane and the modified porous layer. With this, extremely excellent peel strength can be obtained.
- the projection referred to in the present invention is essentially different from the projection obtained by adding, for example, inorganic particles to the laminated polyolefin microporous film.
- the protrusions obtained by adding inorganic particles to the laminated polyolefin microporous membrane are usually extremely small in height, and if a protrusion with a height of 0.5 ⁇ m or more is to be formed by the same means, the laminated polyolefin microporous film It is necessary to add particles having a particle size equal to or greater than the thickness of the film. However, when such particles are added, the strength of the laminated polyolefin microporous film is lowered, which is not realistic.
- the protrusions referred to in the present invention are those in which a part of the surface layer of the laminated polyolefin microporous membrane is grown to a moderately raised shape, and do not deteriorate the basic characteristics of the laminated polyolefin microporous membrane. .
- the irregularly scattered protrusions referred to in the present invention are arranged with regularity or periodicity obtained by passing through an embossing roll before or after the stretching process in the production of a laminated polyolefin microporous film. It is clearly different from the protrusion. Press work such as embossing is basically not preferred because it forms protrusions by compressing and tends to cause a decrease in air resistance and electrolyte permeability.
- the moderately shaped protrusion as used in the present invention means a protrusion having a size of 5 ⁇ m or more and 50 ⁇ m or less and a height of 0.5 ⁇ m or more. That is, 5 ⁇ m ⁇ W ⁇ 50 ⁇ m (W is the size of the protrusion) and 0.5 ⁇ m ⁇ H (H is the height of the protrusion).
- Such protrusions function as anchors when the modified porous layer is laminated on the laminated polyolefin microporous membrane, and as a result, the battery separator having a large 0 ° peel strength is obtained.
- the upper limit of the height is not particularly limited, but 3.0 ⁇ m is sufficient.
- the 0 ° peel strength is affected by the number of protrusions having a height of 0.5 ⁇ m or more and the average height thereof.
- the lower limit of the number of protrusions is preferably 3 / cm 2 , more preferably 5 / cm 2 , and still more preferably 10 / cm 2 .
- the upper limit of the number of protrusions is preferably 200 / cm 2 , more preferably 150 / cm 2 .
- the lower limit of the height of the protrusion is preferably 0.5 ⁇ m, more preferably 0.8 ⁇ m, and still more preferably 1.0 ⁇ m.
- protrusion in this invention say the value measured with the measuring method mentioned later.
- the increasing range of the air resistance referred to in the present invention means a difference between the air resistance of the laminated polyolefin microporous membrane and the air resistance of the battery separator, and is preferably 90 seconds / 100 cc Air or less. Preferably it is 80 cc Air, more preferably 50 cc Air.
- the upper limit of the thickness of the laminated polyolefin microporous membrane used in the present invention is preferably 25 ⁇ m, more preferably 20 ⁇ m, and even more preferably 16 ⁇ m.
- the lower limit is preferably 7 ⁇ m, more preferably 9 ⁇ m.
- the meltdown temperature of the polyolefin laminated microporous membrane of the present invention is 165 ° C. or higher, more preferably 170 ° C. or higher. If the meltdown temperature is within the above range, the stability of the battery is increased because the dimensional stability is high even at high temperatures.
- the upper limit of the air resistance of the laminated polyolefin microporous membrane is preferably 300 sec / 100 cc Air, more preferably 200 sec / 100 cc Air, still more preferably 150 sec / 100 cc Air, and the lower limit is preferably 50 sec / 100 cc Air, more preferably 70 sec. / 100 cc Air, more preferably 100 sec / 100 cc Air.
- the upper limit of the porosity of the laminated polyolefin microporous membrane is preferably 70%, more preferably 60%, and even more preferably 55%.
- the lower limit is preferably 30%, more preferably 35%, still more preferably 40%.
- the average pore size of the laminated polyolefin microporous membrane greatly affects the pore closing performance, and is preferably 0.01 to 1.0 ⁇ m, more preferably 0.05 to 0.5 ⁇ m, and still more preferably 0.1 to 0. .3 ⁇ m.
- the 0 ° peel strength of the modified porous layer can be sufficiently obtained by the anchor effect of the functional resin, and when the modified porous layer is laminated, The air resistance is not greatly deteriorated, and the response to the temperature of the hole closing phenomenon is not slowed, and the hole closing temperature due to the heating rate is not shifted to a higher temperature side.
- the polyolefin microporous film constituting the A layer of the present invention contains polyethylene as a main component.
- the polyethylene content is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass, based on 100% by mass of the entire polyolefin resin. It is.
- polyethylene high density polyethylene such as density exceeding 0.94 g / cm 3, density polyethylene in the range density of 0.93 ⁇ 0.94g / cm 3, density of from 0.93 g / cm 3
- low density polyethylene linear low density polyethylene, ultra high molecular weight polyethylene and the like
- the ultra high molecular weight polyethylene may be not only a homopolymer of ethylene but also a copolymer containing a small amount of other ⁇ -olefin.
- the ⁇ -olefin include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, styrene and the like.
- the laminated film particularly when produced by a coextrusion method, it may be difficult to control the physical property unevenness in the width direction due to the difference in viscosity of each layer, but by using ultrahigh molecular weight polyethylene for the A layer, Since the molecular network of the entire membrane is strengthened, non-uniform deformation hardly occurs, and a microporous membrane having excellent physical property uniformity can be obtained.
- the weight average molecular weight (hereinafter referred to as Mw) of the high density polyethylene is preferably 1 ⁇ 10 5 or more, more preferably 2 ⁇ 10 5 or more.
- the upper limit is preferably 8 ⁇ 10 5 for Mw, more preferably 7 ⁇ 10 5 for Mw. If Mw is in the above range, the stability of the film formation and the finally obtained puncture strength can both be achieved.
- the Mw of the ultra high molecular weight polyethylene is preferably 1 ⁇ 10 6 or more and less than 4 ⁇ 10 6 .
- the Mw of the ultra high molecular weight polyethylene having an Mw of 1 ⁇ 10 6 or more and less than 4 ⁇ 10 6 , the pores and fibrils can be miniaturized and the puncture strength can be increased. Further, if Mw is 4 ⁇ 10 6 or more, the viscosity of the melt becomes too high, so that there may be a problem in the film forming process such that the resin cannot be extruded from the die.
- the content of ultrahigh molecular weight polyethylene is 100% by mass with respect to the entire polyolefin resin, and the lower limit is preferably 2% by mass, more preferably 18% by mass.
- the upper limit is preferably 45% by mass, more preferably 40% by mass. Within this range, both puncture strength and air resistance can be easily achieved.
- the content of the ultrahigh molecular weight polyethylene is within the preferred range, a sufficiently high protrusion can be obtained.
- the modified porous layer is laminated by the protrusions, the protrusions function as anchors, and extremely strong peeling resistance can be obtained against the force applied in parallel to the surface direction of the polyethylene porous film. Further, even when the thickness of the polyethylene porous film is reduced, sufficient tensile strength can be obtained.
- the tensile strength has no particular upper limit, but is preferably 100 MPa or more.
- the B layer of the present invention is a microporous film mainly composed of polyolefin.
- the B layer preferably contains 50% by mass or more of high-density polyethylene from the viewpoint of strength.
- the weight average molecular weight (hereinafter referred to as Mw) of the high density polyethylene is preferably 1 ⁇ 10 5 or more, more preferably 2 ⁇ 10 5 or more.
- the upper limit of Mw is preferably 8 ⁇ 10 5 for Mw, more preferably 7 ⁇ 10 5 for Mw. If Mw is in the above range, the stability of the film formation and the finally obtained puncture strength can both be achieved.
- the B layer contains polypropylene.
- polypropylene When polypropylene is added, the meltdown temperature can be further improved when the polyolefin microporous membrane of the present invention is used as a battery separator.
- a block copolymer and a random copolymer can be used in addition to the homopolymer.
- the block copolymer and random copolymer can contain a copolymer component with an ⁇ -olefin other than propylene, and ethylene is preferable as the other ⁇ -olefin.
- the Mw of polypropylene is preferably 5 ⁇ 10 5 or more, more preferably 6.5 ⁇ 10 5 or more, and further preferably 8 ⁇ 10 5 or more. When Mw is within the above range, a film having a uniform film thickness can be obtained without deteriorating the dispersibility of polypropylene during sheet formation.
- the heat of fusion ( ⁇ Hm) of polypropylene is preferably 90 J / g or more, more preferably 95 J / g. When ⁇ Hm is within the above preferred range, good meltdown characteristics can be obtained.
- the content of polypropylene is preferably less than 60% by mass relative to the total mass of the polyolefin composition. If it is 60% by mass or more, the permeability may be deteriorated. In particular, in the case where the surface layer is a B layer, the amount of powder generated due to polypropylene dropping when the laminated microporous membrane is slitted increases. If the amount of powder generated due to the falling off of polypropylene is large, defects such as pinholes and black spots may occur in the laminated microporous film.
- the lower limit of the addition amount is preferably 3% by mass or more, more preferably 10% by mass, and still more preferably 20% by mass or more. When the content of polypropylene is within the above preferred range, good meltdown characteristics can be obtained.
- the B layer also contains ultrahigh molecular weight polyolefin.
- the ultra high molecular weight polyolefin include ultra high molecular weight polyethylene and ultra high molecular weight polypropylene exemplified in the A layer.
- the polyolefin microporous membrane of the present invention is an antioxidant, a heat stabilizer, an antistatic agent, an ultraviolet absorber, and further an antiblocking agent and a filling material, as long as both the A layer and the B layer do not impair the effects of the present invention.
- Various additives such as materials may be included.
- an antioxidant for the purpose of suppressing oxidative deterioration due to the thermal history of the polyolefin resin.
- Appropriate selection of the type and amount of the antioxidant and heat stabilizer is important for adjusting or enhancing the characteristics of the microporous membrane.
- the laminated polyolefin microporous membrane used in the present invention preferably contains substantially no inorganic particles.
- substantially free of inorganic particles means, for example, a content that is 50 ppm or less, more preferably 10 ppm or less, and even more preferably a detection limit or less when inorganic elements are quantified by fluorescent X-ray analysis. To do. Even if particles are not actively added to the laminated polyolefin microporous membrane, contaminants derived from foreign substances and dirt attached to the lines and equipment in the manufacturing process of the raw resin or polyolefin microporous membrane are peeled off. It may be mixed in the film and may be detected at 50 ppm or less.
- the ratio (Mw / Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polyolefin resin composition of the B layer together with the A layer is preferably in the range of 5 to 200, more preferably 10 to 100. is there.
- Mw / Mn is the above preferred range, extrusion of the polyolefin solution is easy. Further, the polyolefin microporous membrane can obtain a sufficient number of protrusions on the surface, and sufficient mechanical strength can be obtained even when the thickness of the polyolefin microporous membrane is reduced.
- Mw / Mn is used as a measure of molecular weight distribution.
- Mw / Mn of a single polyolefin can be appropriately adjusted by multistage polymerization of polyolefin.
- Mw / Mn of the mixture of polyolefin can be suitably adjusted by adjusting the molecular weight and mixing ratio of each component.
- the present inventors consider the mechanism by which protrusions are formed in the present invention as follows.
- the resin solution of the melted polyolefin resin and the molding solvent is extruded from the die, and at the same time, the crystallization of the polyolefin is started.
- the crystallization rate is increased by contacting the cooling roll and quenching.
- a spherulite having a symmetric structure having a crystal nucleus is formed (FIG. 2).
- the heat transfer rate between the cooling roll surface and the molten polyolefin resin is relatively low, the crystallization rate is low, and as a result, spherulites having relatively small crystal nuclei are formed.
- the spherulite When the heat transfer rate is high, the spherulite has a relatively large crystal nucleus.
- the crystal nuclei of these spherulites become protrusions during TD (width direction) and / or MD (machine direction) stretching, which is a subsequent process.
- Spherulites appear as ring-shaped marks on the surface of the laminated polyolefin microporous membrane (FIG. 3).
- a laminated polyolefin microporous membrane can be freely selected according to the purpose as long as it satisfies the above various characteristics.
- Microporous membrane production methods include the foaming method, phase separation method, dissolution recrystallization method, stretch pore opening method, powder sintering method, etc. Among these, in terms of homogenizing fine pores and cost, A separation method is preferred.
- a polyolefin resin and a molding solvent are heated and melt-kneaded, and the obtained molten mixture is extruded from a die and cooled to form a gel-like molded product, and the obtained gel-like product is obtained.
- examples include a method of obtaining a microporous film by stretching the molded product in at least a uniaxial direction and removing the molding solvent.
- the method for producing a laminated polyolefin microporous membrane of the present invention includes the following steps (a) to (f).
- Step of stretching in the width direction to obtain a laminated stretched molded product Step of extracting and removing the molding solvent from the laminated stretched molded product and drying to obtain a laminated porous molded product ( )
- a step of heat-treating the laminated porous molded article to obtain a laminated polyolefin microporous membrane before the step (a), during the steps (a) to (f), or after the step (f), a hydrophilic treatment, Other steps such as charge removal processing can be added. Moreover, a redrawing process can also be provided after a process (f).
- a molding solvent for example, nonane, decane, undecane, dodecane, liquid paraffin and other aliphatic or cyclic hydrocarbons, or mineral oil fractions with boiling points corresponding to these, gel-like molded products with a stable solvent content
- Nonvolatile solvents such as liquid paraffin are preferred for obtaining.
- the dissolution by heating is performed by a method in which the polyolefin composition is dissolved at a temperature at which the polyolefin composition is completely dissolved by stirring or uniformly mixing in an extruder.
- the temperature varies depending on the polymer and solvent to be used when it is dissolved in an extruder or in a solvent while stirring, but it is preferably in the range of 140 to 250 ° C., for example.
- the concentration of the polyolefin resin is preferably 15 to 40% by mass, more preferably 25 to 40% by mass, and further preferably 28 to 35% by mass, where the total of the polyolefin resin and the molding solvent is 100% by mass.
- concentration of the polyolefin resin is within the above preferable range, a sufficient number of crystal nuclei for forming protrusions are formed, and a sufficient number of protrusions are formed. Further, swell and neck-in are suppressed at the die outlet when extruding the polyolefin resin solution, and the moldability and self-supporting property of the extruded molded body are maintained.
- a laminated microporous membrane having a structure (gradient structure) in which the average pore diameter is changed in the film thickness direction can be obtained.
- the average pore diameter of the layer formed using the resin solution having the lower concentration is larger than the average pore diameter of the layer formed using the resin solution having the higher concentration.
- Which concentration of the resin solution A or B is to be increased can be appropriately selected according to the physical properties required for the laminated microporous membrane. For example, if the inner layer is a dense structure layer of 0.01 to 0.05 ⁇ m and the surface layer is a coarse structure layer 1.2 to 5.0 times the dense structure layer, the balance between ion permeability and pin puncture strength is improved. be able to.
- the method of melt kneading is not particularly limited, but is usually performed by uniformly kneading in an extruder. This method is suitable for preparing highly concentrated solutions of polyolefins.
- the melt kneading temperature varies depending on the polyolefin resin used. For example, since the polyethylene composition has a melting point of about 130 to 140 ° C., the lower limit of the melt kneading temperature is preferably 140 ° C., more preferably 160 ° C., and most preferably 170 ° C. The upper limit is preferably 250 ° C, 230 ° C, and most preferably 200 ° C.
- the polyolefin solution contains polypropylene, and the melt kneading temperature in that case is preferably 190 to 270 ° C.
- the melt kneading temperature is preferably low, but if it is lower than the above-mentioned temperature, an unmelted product is generated in the extrudate extruded from the die, causing film breakage or the like in the subsequent stretching step. It may be a cause.
- the temperature is higher than the above-described temperature, the thermal decomposition of the polyolefin becomes violent, and the properties of the resulting microporous film, for example, puncture strength, tensile strength, etc., may be inferior.
- the ratio (L / D) of the screw length (L) to the diameter (D) (L / D) of the twin screw extruder is preferably 20 to 100 from the viewpoint of obtaining good process kneadability and resin dispersibility / distributability.
- the lower limit is more preferably 35.
- the upper limit value is more preferably 70.
- L / D is 20 or more, melt-kneading is sufficient.
- L / D is 100 or less, the residence time of the polyolefin solution does not increase excessively.
- the inner diameter of the twin-screw extruder is preferably 40 to 100 mm.
- the screw rotation speed (Ns) of the twin screw extruder is 150 rpm or more.
- Ratio of extrusion rate Q (kg / h) of polyolefin solution to Ns (rpm), Q / Ns is preferably 0.64 kg / h / rpm or less, more preferably 0.35 kg / h / rpm or less.
- the polyolefin resin solutions A and B obtained in (a) and (b) are extruded from a die, and at least one of them is a cooling roll having a surface from which the molding solvent is removed by the molding solvent removing means.
- the step of cooling and forming a laminated gel-like molded product The polyolefin resin solutions A and B melted and kneaded by an extruder are pushed up from a die directly or through another extruder and cooled by a cooling roll. Then, a laminated gel-like molded product is formed.
- a method for obtaining a laminated gel-like molded product it is desirable to separately prepare gel-like molded products to be laminated, and then stick them together through a calender roll or the like (sticking method), or supply a polyolefin solution separately to an extruder as desired. Any method may be used such as a method of melting at a temperature of 5 ° C, joining in a polymer tube or die, coextrusion and laminating, and then forming a laminated gel-like molded product (coextrusion method). From the viewpoint of adhesion, it is preferable to use a coextrusion method.
- the gel-like molded product is formed by bringing the polyolefin resin solution extruded from the die into contact with a rotating cooling roll set at a surface temperature of 20 ° C. to 40 ° C. with a refrigerant.
- the extruded polyolefin resin solution is preferably cooled to 25 ° C. or lower.
- the cooling rate in the temperature range where crystallization is substantially performed becomes important.
- the extruded polyolefin resin solution is cooled at a cooling rate of 10 ° C./second or more in a temperature range where crystallization is substantially carried out to obtain a gel-like molded product.
- the cooling rate is preferably 20 ° C./second or more, more preferably 30 ° C./second or more, and further preferably 50 ° C./second or more.
- the cooling rate can be estimated by simulating from the extrusion temperature of the gel-shaped molded product, the thermal conductivity of the gel-shaped molded product, the thickness of the gel-shaped molded product, the molding solvent, the cooling roll, and the heat transfer coefficient of air.
- the polyolefin resin solution is cooled by being wound around a rotating cooling roll to become a gel-like molded product, but the molding solvent adheres to the surface of the cooling roll after the gel-like molded product is pulled apart.
- the polyolefin resin solution is cooled by being wound around a rotating cooling roll to become a gel-like molded product, but the molding solvent adheres to the surface of the cooling roll after the gel-like molded product is pulled apart.
- the cooling rate becomes slow due to the heat insulating effect, and it becomes difficult to form protrusions. Therefore, it is important to remove the forming solvent as much as possible before the cooling roll comes into contact with the polyolefin resin solution again.
- the method for removing the molding solvent that is, the method for removing the molding solvent from the cooling roll is not particularly limited, but the doctor blade is placed on the cooling roll so as to be parallel to the width direction of the gel-like molded article and passed through the doctor blade.
- a method is preferably employed in which the molding solvent is scraped off to the extent that the cooling roll surface is invisible until immediately after the gel-like molded product comes into contact.
- it can be removed by means such as blowing with compressed air, suction, or a combination of these methods.
- the method of scraping off using a doctor blade is preferable because it can be carried out relatively easily, and it is more preferable to use a plurality of doctor blades in order to improve the removal efficiency of the forming solvent.
- the material of the doctor blade is not particularly limited as long as it is resistant to the molding solvent, but is preferably made of resin or rubber rather than metal. If it is made of metal, the cooling roll may be scratched.
- the resin doctor blade include polyester, polyacetal, and polyolefin.
- the thickness of the polyolefin resin solution during extrusion is preferably 1500 ⁇ m or less, more preferably 1000 ⁇ m or less, and still more preferably 800 ⁇ m or less.
- the cooling rate on the surface on the side of the cooling roll is preferably not slow.
- the bonding method when a laminated gel-like molded product is obtained by the bonding method, if at least one of the polyolefin resin solutions to be the A layer or the B layer is formed as a gel-like molded product under the above cooling conditions. Good.
- the bonding together it is necessary to laminate
- the polyolefin resin solution laminated and extruded from the die may be formed as a laminated gel-like molded product under the above cooling conditions.
- the laminated polyolefin is a porous laminate comprising at least an A layer and a B layer.
- the layer configuration of the laminated polyolefin may be at least two layers of the A layer and the B layer from the viewpoint of physical properties balance such as shutdown characteristics and strength and permeability, but from the viewpoint of the front and back balance of the final film, A three-layer structure of A layer / B layer / A layer or B layer / A layer / B layer is more preferable.
- the protrusions may be formed on either the A layer or the B layer, but from the viewpoint of the balance between permeability and strength, the surface layer is the A layer,
- the inner layer is preferably a B layer.
- the surface layer is B and the inner layer is A.
- the thickness of layer B of the laminated polyolefin microporous membrane is preferably 3 ⁇ m or more and 15 ⁇ m or less.
- the upper limit is more preferably 10 ⁇ m, further preferably 7 ⁇ m, and further preferably 6 ⁇ m.
- the lower limit is preferably 4 ⁇ m.
- the thickness of the B layer refers to the total thickness of each B layer when the laminated polyolefin microporous membrane has two or more B layers.
- the laminated gel-like molded product is stretched to obtain a stretched molded product. Stretching is performed by heating the gel-like molded product and performing normal tenter method, roll method, or a combination of these methods at a predetermined magnification in two directions of MD and TD.
- the stretching may be either simultaneous stretching (simultaneous biaxial stretching) or sequential stretching in MD and TD (machine direction and width direction). In the sequential stretching, the order of MD and TD is not limited, and at least one of MD and TD may be stretched in multiple stages.
- the draw ratio varies depending on the thickness of the original fabric, but is preferably 9 times or more, more preferably 16 to 400 times in terms of surface magnification.
- stretching at the same magnification of MD and TD such as 3 ⁇ 3, 5 ⁇ 5, or 7 ⁇ 7 is preferable.
- the surface magnification is in the above preferred range, stretching is sufficient and a highly elastic, high strength microporous membrane can be obtained.
- a desired air resistance can be obtained by adjusting the stretching temperature.
- the stretching temperature is preferably below the melting point of the polyolefin resin, and more preferably in the range of (polyolefin resin crystal dispersion temperature Tcd) to (polyolefin resin melting point).
- Tcd polyolefin resin crystal dispersion temperature
- the crystal dispersion temperature Tcd is determined from the temperature characteristics of dynamic viscoelasticity measured according to ASTM D 4065. Or it may obtain
- (E) A step of extracting and removing the molding solvent from the laminated stretched molded product and drying to obtain a laminated porous molded product.
- the stretched molded product is treated with a washing solvent to remove the remaining molding solvent, A porous membrane is obtained.
- Cleaning solvents include hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as ethane trifluoride, and ethers such as diethyl ether and dioxane. Volatile ones can be used. These cleaning solvents are appropriately selected according to the molding solvent used for dissolving the polyolefin, and are used alone or in combination.
- the cleaning method can be performed by a method of immersing and extracting in a cleaning solvent, a method of showering the cleaning solvent, a method of sucking the cleaning solvent from the opposite side of the stretched molded product, or a method of a combination thereof. Washing as described above is performed until the residual solvent in the stretched molded product, which is a stretched molded product, is less than 1% by mass. Thereafter, the cleaning solvent is dried.
- the cleaning solvent can be dried by heat drying, air drying, or the like.
- (F) Step of heat-treating the laminated porous molded product to obtain a laminated polyolefin microporous membrane The laminated porous molded product obtained by drying is heat-treated to obtain a laminated polyolefin microporous membrane.
- the heat treatment temperature is preferably 90 to 150 ° C. When the heat treatment temperature is in the above preferred range, the heat shrinkage rate of the obtained laminated polyolefin microporous membrane can be reduced, and the air resistance can be ensured.
- the heat treatment time is not particularly limited, but it is usually preferably 1 second to 10 minutes, more preferably 3 seconds to 2 minutes. For the heat treatment, any of a tenter method, a roll method, a rolling method, and a free method can be adopted.
- the heat treatment step it is preferable to grip in both the MD (machine direction) and TD (width direction) directions and contract in at least one direction of MD and TD.
- the contraction rate for contracting in at least one direction of MD and TD is preferably 0.01 to 50%, more preferably 3 to 20%.
- the shrinkage rate is within the above preferable range, the thermal shrinkage rate at 105 ° C. and 8 hours is improved, and the air resistance is maintained.
- TD or MD may be further performed before the heat treatment, or redrawing of about 5% to 20% in both directions may be performed.
- the microporous membrane may be hydrophilized.
- the hydrophilic treatment can be performed by monomer grafting, surfactant treatment, corona discharge or the like. Monomer grafting is preferably performed after the crosslinking treatment.
- the corona discharge treatment can be performed in air, nitrogen, or a mixed atmosphere of carbon dioxide and nitrogen.
- the modified porous layer used in the present invention is preferably laminated on the side having the protrusions of the laminated polyolefin microporous membrane.
- the modified porous layer is provided on both sides of the laminated polyolefin microporous membrane, the modified porous layer on the side to which the parallel stress is more strongly applied by the contact of a roll or a bar in the subsequent process such as the slitting process or the conveying process.
- Lamination is preferably performed on the side of the laminated polyolefin microporous membrane having the protrusions because the effect of the present invention is exhibited.
- the modified porous layer referred to in the present invention imparts or improves at least one function such as heat resistance, adhesion to an electrode material, and electrolyte permeability.
- the modified porous layer contains inorganic particles and a binder having a tensile strength of 5 N / mm 2 or more.
- a binder having a tensile strength of 5 N / mm 2 or more By using a binder having a tensile strength of 5 N / mm 2 or more, a battery separator having an extremely excellent 0 ° peel strength can be obtained by the synergistic effect of the protrusions present on the surface of the laminated polyolefin microporous membrane and the tensile strength of the binder. .
- the battery separator does not significantly increase the air resistance as compared with the case of the laminated polyolefin microporous membrane alone. This is because sufficient 0 ° peel strength can be obtained without allowing a large amount of binder to penetrate into the pores of the laminated polyolefin microporous membrane.
- Tensile strength of the binder is at 5N / mm 2 or more, the lower limit is preferably 10 N / mm 2, more preferably 20 N / mm 2, more preferably 30 N / mm 2. There is no particular upper limit, but 100 N / mm 2 is sufficient.
- the tensile strength of the binder refers to a value measured by the method described later.
- the use tensile strength of 5N / mm 2 or more binders in the present invention although the tensile strength is not particularly limited as long as 5N / mm 2 or more, e.g., polyvinyl alcohol, cellulose ether resins, and acrylic resins .
- the cellulose ether resin include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanethyl cellulose, oxyethyl cellulose and the like.
- the acrylic resin a cross-linked acrylic resin is preferable. Commercially available aqueous solutions or aqueous dispersions can also be used.
- Examples of commercially available products include “POVACOAT” (registered trademark) manufactured by Nisshin Kasei Co., Ltd., “Jurimer” (registered trademark) AT-510, ET-410, FC-60 manufactured by Toa Gosei Co., Ltd.
- Examples include SEK-301, UW-223SX, UW-550CS manufactured by Taisei Fine Chemical Co., Ltd., WE-301, EC-906EF, CG-8490 manufactured by DIC Corporation.
- polyvinyl alcohol and acrylic resins having electrode adhesion, high affinity with non-aqueous electrolytes, suitable heat resistance, and relatively high tensile strength are preferable.
- the coating liquid for forming the modified porous layer contains inorganic particles.
- the coating liquid in this specification contains a binder having a tensile strength of 5 N / mm 2 or more, inorganic particles, and a solvent capable of dissolving or dispersing the binder, and is used for forming a modified porous layer.
- the binder has at least a role of bonding inorganic particles and a role of bonding the laminated polyolefin microporous membrane and the modified porous layer.
- the solvent include water, alcohols, acetone, and n-methylpyrrolidone.
- the effect of preventing internal short circuit (dendrite prevention effect) due to the growth of the dendritic crystals of the electrode inside the battery, the effect of reducing the heat shrinkage, and the provision of slipperiness are also obtained. be able to.
- the upper limit of the amount of added particles is preferably 98% by mass, more preferably 95% by mass.
- the lower limit is preferably 80% by mass, and more preferably 85% by mass.
- the average particle size of the inorganic particles is preferably 1.5 times or more and 50 times or less, more preferably 2.0 times or more and 20 times or less of the average pore size of the laminated polyolefin microporous membrane.
- the average particle diameter of the particles is within the above-mentioned preferable range, an increase in the air resistance due to blocking the pores of the laminated polyolefin microporous film in a state where the heat-resistant resin and the particles are mixed is prevented, and further, the battery This prevents the particles from falling off during the assembly process, leading to serious battery defects.
- Inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite , Molybdenum sulfide, mica, boehmite and the like.
- the heat-resistant crosslinked polymer particles include crosslinked polystyrene particles, crosslinked acrylic resin particles, and crosslinked methyl methacrylate particles.
- Examples of the shape of the inorganic particles include a true spherical shape, a substantially spherical shape, a plate shape, a needle shape, and a polyhedral shape, but are not particularly limited.
- the solid content concentration of the coating solution is not particularly limited as long as it can be uniformly applied, but is preferably 50% by mass or more and 98% by mass or less, and more preferably 80% by mass or more and 95% by mass or less.
- the solid content concentration of the coating solution is in the above preferred range, the modified porous layer is prevented from becoming brittle, and a sufficient peel strength of 0 ° of the modified porous layer can be obtained.
- the film thickness of the modified porous layer is preferably 1 to 5 ⁇ m, more preferably 1 to 4 ⁇ m, and still more preferably 1 to 3 ⁇ m.
- the battery separator obtained by laminating the modified porous layer can ensure the film breaking strength and insulation when melted / shrinked at the melting point or higher, and A sufficient pore blocking function can be obtained and abnormal reactions can be prevented.
- the winding volume can be suppressed, which is suitable for increasing the battery capacity. In addition, suppressing curling leads to improved productivity in the battery assembly process.
- the porosity of the modified porous layer is preferably 30 to 90%, more preferably 40 to 70%.
- the desired porosity can be obtained by appropriately adjusting the concentration of inorganic particles, the binder concentration, and the like.
- the battery separator obtained by laminating the modified porous layer has a low electrical resistance of the membrane, a large current flows easily, and the membrane strength is maintained.
- the upper limit of the total film thickness of the battery separator obtained by laminating the modified porous layer is preferably 25 ⁇ m, more preferably 20 ⁇ m.
- the lower limit is preferably 6 ⁇ m or more, more preferably 7 ⁇ m or more.
- the air resistance of the battery separator is one of the most important characteristics, and is preferably 50 to 400 sec / 100 cc Air, more preferably 100 to 350 sec / 100 cc Air, and further preferably 100 to 300 sec / 100 cc Air.
- the desired air resistance can be obtained by adjusting the porosity of the modified porous layer and adjusting the degree of penetration of the binder into the laminated polyolefin microporous membrane.
- the air permeability resistance of the battery separator is within the above preferable range, sufficient insulation is obtained, and foreign matter clogging, short circuit and film breakage are prevented. Further, by suppressing the film resistance, charge / discharge characteristics and life characteristics within a practically usable range can be obtained.
- the method for laminating the modified porous layer on the laminated polyolefin microporous membrane of the present invention comprises the following step (g).
- (G) A coating liquid containing a binder having a tensile strength of 5 N / mm 2 or more, an inorganic particle, and a solvent capable of dissolving or dispersing the binder on the surface of the laminated polyolefin microporous film in contact with the cooling roll. The process of forming a laminated film and drying.
- the coating solution is applied to the laminated polyolefin microporous film by a method described later so as to have a predetermined film thickness, and the drying temperature is 40 to 80 ° C. and the drying time is 5 seconds to 60 seconds. It can be obtained by a drying method.
- a coating solution in which the binder is soluble and dissolved in a solvent miscible with water is laminated on a predetermined laminated polyolefin microporous film using a coating method described later, and is placed in a specific humidity environment. It is also possible to use a method in which the solvent to be mixed is phase-separated and the binder is further solidified by adding it to a water bath (coagulation bath).
- Examples of methods for applying the coating liquid include reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, Mayer bar coating method, pipe doctor method, blade coating. Method, die coating method and the like, and these methods can be carried out singly or in combination.
- the battery separator of the present invention is desirably stored in a dry state, but when it is difficult to store in a completely dry state, it is preferable to perform a vacuum drying treatment at 100 ° C. or lower immediately before use.
- the battery separator of the present invention includes a nickel-hydrogen battery, a nickel-cadmium battery, a nickel-zinc battery, a silver-zinc battery, a secondary battery such as a lithium secondary battery, a lithium polymer secondary battery, and a plastic film capacitor, ceramic Although it can be used as a separator for a capacitor, an electric double layer capacitor, etc., it is particularly preferably used as a separator for a lithium ion secondary battery.
- a lithium ion secondary battery will be described as an example.
- a positive electrode and a negative electrode are laminated via a separator, and the separator contains an electrolytic solution (electrolyte).
- the structure of the electrode is not particularly limited, and may be a known structure.
- the positive electrode usually has a current collector and a positive electrode active material layer containing a positive electrode active material capable of occluding and releasing lithium ions formed on the surface of the current collector.
- the positive electrode active material include transition metal oxides, composite oxides of lithium and transition metals (lithium composite oxides), inorganic compounds such as transition metal sulfides, and the like.
- the transition metal include V, Mn, Fe, Co, and Ni.
- Preferred examples of the lithium composite oxide among the positive electrode active materials include lithium nickelate, lithium cobaltate, lithium manganate, and a layered lithium composite oxide based on an ⁇ -NaFeO 2 type structure.
- the negative electrode has a current collector and a negative electrode active material layer including a negative electrode active material formed on the surface of the current collector.
- the negative electrode active material include carbonaceous materials such as natural graphite, artificial graphite, cokes, and carbon black.
- the electrolytic solution can be obtained by dissolving a lithium salt in an organic solvent.
- Lithium salts include LiClO 4 , LiPF 6 , LiAsF 6 , LiSbF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiC (CF 3 SO 2 ) 3 , Li 2 B 10 Cl 10 , Examples include LiN (C 2 F 5 SO 2 ) 2 , LiPF 4 (CF 3 ) 2 , LiPF 3 (C 2 F 5 ) 3 , lower aliphatic carboxylic acid lithium salt, LiAlCl 4 and the like. These may be used alone or in admixture of two or more.
- organic solvent examples include high boiling point and high dielectric constant organic solvents such as ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and ⁇ -butyrolactone, and tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, dioxolane, dimethyl carbonate, diethyl carbonate, and the like.
- organic solvents having a low boiling point and a low viscosity These may be used alone or in admixture of two or more.
- a high dielectric constant organic solvent has a high viscosity
- a low viscosity organic solvent has a low dielectric constant. Therefore, it is preferable to use a mixture of both.
- the separator of the present invention can be impregnated with an electrolytic solution to impart ion permeability to the separator.
- the impregnation treatment is performed by immersing the microporous membrane in an electrolytic solution at room temperature.
- a battery can be obtained by inserting this electrode element into a battery can, impregnating with the above electrolyte, and caulking a battery lid also serving as a positive electrode terminal provided with a safety valve via a gasket.
- the measured value in an Example is a value measured with the following method.
- protrusions The number and size of protrusions were measured after stabilizing the light source using a confocal microscope (HD100 manufactured by Lasertec Corporation) placed on a base isolation table.
- a confocal microscope HD100 manufactured by Lasertec Corporation
- a 1 cm ⁇ 1 cm square frame was drawn with an ultrafine oil pen on the surface of the laminated polyolefin microporous membrane obtained in Examples and Comparative Examples that was in contact with a cooling roll during film formation.
- the surface on which the square frame was drawn was placed on the sample stage, and was fixed to the sample stage using an electrostatic contact apparatus attached to the confocal microscope.
- a ring-shaped trace derived from a polyolefin spherulite as shown in FIG. 3 is displayed on a monitor as a two-dimensional image (referred to as a REAL screen in this apparatus).
- the position of the sample stage was adjusted so that the darkest part of was positioned almost at the center of the monitor screen.
- the object of the projection height measurement was such that the major axis of the ring-shaped mark derived from the polyolefin spherulites was 0.2 mm or more.
- the cursor was placed on both ends of the ring in the major axis direction in the two-dimensional image, and the length was read.
- REFSET This device is referred to as REFSET.
- the measurement range in the height direction was set to 15 ⁇ m above and below, with the reference height being 0 ⁇ m. Also, the scan time was 120 seconds, the STEP moving distance was 0.1 ⁇ m / Step, and the three-dimensional data was captured.
- a data processing image (referred to as a Z image in the present apparatus) was displayed and smoothing processing was performed (smoothing condition: filter size 3 ⁇ 3, matrix type SMOOTH3-0, once). In addition, horizontal correction was performed on the horizontal correction screen as necessary.
- a cursor was placed in a horizontal direction at a position (the brightest part) passing through the highest protrusion in the data processing image, and a cross-sectional profile corresponding to the cursor was displayed on the cross-sectional profile image.
- the two cursors were aligned with the inflection points of the sleeves of the protrusions in the vertical direction, and the distance between the cursors was taken as the protrusion size.
- FIG. 1 schematically shows the evaluation method.
- 1 is a laminated sample
- 2 is a laminated polyolefin microporous membrane
- 3 is a modified porous layer
- 4 is a double-sided pressure-sensitive adhesive tape
- a double-sided adhesive tape (NW-K50 manufactured by Nichiban Co., Ltd.) 4 having the same size was attached to an aluminum plate 5 having a size of 50 mm ⁇ 25 mm and a thickness of 0.5 mm.
- the surface of the laminated polyolefin microporous membrane 2 of Sample 1 (battery separator) cut out to a width of 50 mm and a length of 100 mm is pasted on the aluminum plate 5 so that 40 mm overlaps from the edge of one side of the 25 mm length. Attached and cut off the protruding part. Next, a double-sided adhesive tape is attached to one side of an aluminum plate 5 ′ having a length of 100 mm, a width of 15 mm, and a thickness of 0.5 mm, so that 20 mm overlaps from the end of one side of the 25 mm long sample side of the aluminum plate 5. Pasted on.
- the aluminum plate 5 and the aluminum plate 5 ′ sandwiching the sample are attached to a tensile testing machine (Autograph AGS-J load cell capacity 1 kN, manufactured by Shimadzu Corporation), and the aluminum plate 5 and the aluminum plate 5 ′ are opposite in parallel.
- the film was pulled in the direction at a pulling speed of 10 mm / min, and the strength when the modified porous layer was peeled was measured. This measurement was performed for three arbitrary points spaced 30 cm or more in the longitudinal direction, and the average value was defined as 0 ° peel strength of the modified porous layer.
- Average pore diameter The average pore diameter of the laminated polyolefin microporous membrane was measured by the following method. The sample was fixed on the measurement cell using double-sided tape, platinum or gold was vacuum-deposited for several minutes, and the surface of the film was subjected to SEM measurement at an appropriate magnification. Arbitrary ten places were selected on the image obtained by SEM measurement, and the average value of the pore diameters at these ten places was taken as the average pore diameter of the sample.
- Air permeability resistance (sec / 100ccAir) Using a Gurley Densometer Type B manufactured by Tester Sangyo Co., Ltd., fix the laminated polyolefin microporous membrane or battery separator so that there are no wrinkles between the clamping plate and the adapter plate, and in accordance with JIS P8117 It was measured.
- the sample was a 10 cm square, the measurement points were a total of 5 points at the center and 4 corners of the sample, and the average value was used as the air resistance. When the length of one side of the sample is less than 10 cm, a value obtained by measuring five points at intervals of 5 cm may be used.
- the increase width of the air permeability resistance was obtained from the following formula.
- meltdown temperature Using a thermomechanical analyzer (Seiko Denshi Kogyo Co., Ltd., TMA / SS6000), pulling a 10 mm (TD) ⁇ 3 mm (MD) test piece in the longitudinal direction of the test piece with a constant load of 2 gf The temperature at which the temperature was raised from room temperature at a rate of 5 ° C./min and the film was broken by melting was taken as the meltdown temperature.
- a linear baseline is set in the range of 85 to 175 ° C, and the calorific value is calculated from the area surrounded by the linear baseline and the DSC curve. Converted per sample mass.
- the evaluation area was 100 mm wide ⁇ 500 m long. (When the width was less than 100 mm, the length was adjusted so that the same evaluation area was obtained.) Judgment criteria ⁇ (very good): 5 or less ⁇ (good): 6 to 15 ⁇ (defect): 16 or more
- Weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) Mw and Mw / Mn were determined by gel permeation chromatography (GPC) method under the following conditions.
- GPC gel permeation chromatography
- ⁇ Measurement device GPC-150C manufactured by Waters Corporation Column: “Shodex” (registered trademark) UT806M manufactured by Showa Denko KK -Column temperature: 135 ° C
- Injection volume 500 ⁇ l -Detector: Differential refractometer manufactured by Waters Corporation-Calibration curve: Prepared from a calibration curve obtained using a monodisperse polystyrene standard sample using a predetermined conversion constant.
- Example 1 Tetrakis [methylene as an antioxidant was added to 100 parts by weight of a composition comprising 30% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and 70% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 350,000.
- UHMWPE ultra high molecular weight polyethylene
- HDPE high density polyethylene
- a polyethylene composition A to which 0.375 parts by weight of -3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane was added was obtained. 30 parts by weight of this polyethylene composition A was charged into a twin screw extruder. 70 parts by weight of liquid paraffin was supplied from the side feeder of this twin screw extruder, melted and kneaded, and a polyolefin resin solution A was prepared in the extruder.
- ultra high molecular weight polyethylene with a weight average molecular weight of 2 million is 15% by weight
- high density polyethylene with a weight average molecular weight of 300,000 is 65% by weight
- the weight average molecular weight is 530,000
- the heat of fusion is 96 J /
- a polyolefin composition B was obtained. 25 parts by weight of this polyolefin composition B was charged into a twin screw extruder. 75 parts by weight of liquid paraffin was supplied from the side feeder of this twin-screw extruder, melted and kneaded, and a polyolefin resin solution B was prepared in the extruder.
- the obtained polyolefin resin solutions A and B were coextruded from a multilayer die at 190 ° C. so that the layer structure was A / B / A and the solution ratio was 1/1/1, and the internal cooling water temperature was 25 ° C.
- a laminated gel-like molded product was formed while being taken up by a cooling roll having a diameter of 800 mm kept at the same temperature. At this time, one polyester doctor blade is inserted in the width direction of the gel-shaped molded article between the point where the laminated gel-shaped molded article is separated from the cooling roll and the point where the laminated polyethylene resin solution extruded from the die contacts the cooling roll.
- a microporous membrane was obtained.
- Polyvinyl alcohol (average polymerization degree 1700, saponification degree 99% or more), alumina particles having an average particle diameter of 0.5 ⁇ m, and ion-exchanged water were blended in a weight ratio of 6:54:40, respectively, and zirconium oxide beads (Toray Industries, Inc. ) “Traceram” (registered trademark) beads, 0.5 mm in diameter) and placed in a polypropylene container, and dispersed for 6 hours with a paint shaker (manufactured by Toyo Seiki Seisakusho). Subsequently, it filtered with the filter of 5 micrometers of filtration limits, and obtained the coating liquid (a).
- a coating liquid (a) is applied by gravure coating to the surface of the laminated polyethylene microporous membrane that was in contact with the cooling roll during film formation, and dried by passing through a hot air drying oven at 50 ° C. for 10 seconds.
- a battery separator having a final thickness of 22 ⁇ m was obtained.
- Example 2 A battery separator was obtained in the same manner as in Example 1 except that two polyester doctor blades were applied to the cooling roll at an interval of 20 mm.
- Example 3 A battery separator was obtained in the same manner as in Example 1 except that three polyester doctor blades were each applied to the cooling roll at an interval of 20 mm.
- Example 4 Two-part curable aqueous acrylic urethane resin (solid content concentration 45% by mass) composed of aqueous acrylic polyol and water-dispersible polyisocyanate (curing agent), alumina particles having an average particle size of 0.5 ⁇ m, and ion-exchanged water are respectively 10:40: 50 weight ratio, zirconium oxide beads (Toraysemu "Traceram” (registered trademark) beads, diameter 0.5mm) together with polypropylene container, paint shaker (Toyo Seiki Seisakusho) For 6 hours. Subsequently, it filtered with the filter of 5 micrometers of filtration limits, and obtained the coating liquid (b). A modified porous layer was laminated in the same manner as in Example 1 except that the coating liquid (a) was changed to the coating liquid (b) to obtain a battery separator.
- curing agent aqueous acrylic polyol and water-dispersible polyisocyanate
- POVACOATR polyvinyl alcohol, acrylic acid and methyl methacrylate
- Example 2 The solution was filtered through a filter having a filtration limit of 5 ⁇ m to obtain a coating solution (c).
- a modified porous layer was laminated in the same manner as in Example 1 except that the coating liquid (a) was replaced with the coating liquid (c) to obtain a battery separator.
- Example 6 A battery separator was obtained in the same manner as in Example 2 except that the internal cooling water temperature of the cooling roll was maintained at 35 ° C.
- Example 7 As the polyolefin resin composition B, 5% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million, 55% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 300,000, and a weight average molecular weight of 530,000, A composition obtained by adding 0.375 parts by weight of an antioxidant to 100 parts by weight of a composition composed of 40% by weight of polypropylene having a heat of fusion of 96 J / g and 70 parts by weight of liquid paraffin with respect to 30 parts by weight of polyethylene composition B A separator for a battery was obtained in the same manner as in Example 1 except that the polyolefin resin solution B was obtained by supplying the parts.
- UHMWPE ultra high molecular weight polyethylene
- HDPE high density polyethylene
- Example 8 As polyolefin resin composition A, 100 parts by weight of a composition comprising 20% by weight of ultrahigh molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2 million and 80% by weight of high density polyethylene (HDPE) having a weight average molecular weight of 300,000, The same procedure as in Example 1 was conducted except that a composition to which 0.375 parts by weight of antioxidant was added and 70 parts by weight of liquid paraffin was supplied to 30 parts by weight of polyethylene composition B to obtain polyolefin resin solution B. Thus, a battery separator was obtained.
- UHMWPE ultrahigh molecular weight polyethylene
- HDPE high density polyethylene
- Example 9 A battery separator was obtained in the same manner as in Example 3 except that the extrusion amounts of the polyolefin solutions A and B were adjusted so that the thickness of the polyolefin laminated porous membrane was as shown in the table.
- Example 10 Except for blending ratio of ultrahigh molecular weight polyethylene and high density polyethylene of polyolefin composition A, and not using ultrahigh molecular weight polyethylene for polyolefin composition B, except that the blending ratio of high density polyethylene and polypropylene is as shown in the table.
- a battery separator was obtained in the same manner as in Example 1.
- Example 11 Alumina particles are replaced with crosslinked polymer particles (polymethyl methacrylate-based crosslinked product particles (“Eposter” (registered trademark) MA1002, manufactured by Nippon Shokubai Co., Ltd., average particle size: 2.5 ⁇ m)).
- Varnish (d) was obtained with a blending ratio of -methyl-2-pyrrolidone of 35:10:55 (weight ratio).
- a battery separator was obtained in the same manner as in Example 1 except that the varnish (d) was used.
- Example 12 Fluorine resin solution (“KF polymer” (registered trademark) # 9300 (polyvinylidene fluoride (5% N-methylpyrrolidone solution) manufactured by Kureha Chemical Industry Co., Ltd.) and alumina particles having an average particle size of 0.5 ⁇ m, N-methyl- 2-pyrrolidone was blended at a weight ratio of 16:34:50, respectively, and placed in a polypropylene container together with zirconium oxide beads (“Traceram” (registered trademark) beads, diameter 0.5 mm) manufactured by Toray Industries, Inc.
- KF polymer registered trademark
- # 9300 polyvinylidene fluoride (5% N-methylpyrrolidone solution) manufactured by Kureha Chemical Industry Co., Ltd.
- alumina particles having an average particle size of 0.5 ⁇ m N-methyl- 2-pyrrolidone
- the mixture was dispersed with a shaker (manufactured by Toyo Seiki Seisakusho Co., Ltd.) for 6 hours, and then filtered through a filter with a filtration limit of 5 ⁇ m to obtain varnish (e), which was the same as Example 1 except that varnish (e) was used. Thus, a battery separator was obtained.
- Example 13 Acrylic emulsion (“Polysol” (registered trademark) AT-731 manufactured by Showa Denko KK, nonvolatile content 47%), alumina particles having an average particle size of 0.5 ⁇ m, and ion-exchanged water in a weight ratio of 2:55:43, respectively.
- Polysol registered trademark
- alumina particles having an average particle size of 0.5 ⁇ m
- ion-exchanged water in a weight ratio of 2:55:43, respectively.
- zirconium oxide beads Toraysemu "Traceram” (registered trademark) beads, diameter 0.5mm
- Toyo Seiki Seisakusho Toyo Seiki Seisakusho
- Example 14 A battery separator was obtained in the same manner as in Example 1 except that the coating liquid (g) in which the alumina particles were changed to barium sulfate fine particles (average particle size: 0.3 ⁇ m) was used.
- Comparative Example 1 Except that only the polyethylene solution A was used to extrude from a single-layer die at 190 ° C. to form a single-layer gel-like molding, and the single-layer gel-like molding obtained instead of the laminated gel-like molding was used. A battery separator was obtained in the same manner as in Example 1.
- Comparative Example 2 A battery separator was obtained in the same manner as in Example 8 except that a polypropylene having a weight average molecular weight of 490,000 and a heat of fusion of 70 J / g was used as the polypropylene used for the polyolefin solution B.
- Comparative Example 3 As the polyolefin resin compositions A and B, battery separators were obtained in the same manner as in Example 1 except that the blending ratio, addition amount, and resin concentration were as shown in the table.
- Comparative Example 4 The polyethylene resin solution extruded from the die was cooled with a cooling roll, and when the gel-like molded product was obtained, the doctor blade was not used and the liquid paraffin adhering to the cooling roll was not scraped off. Similarly, a battery separator was obtained.
- Comparative Example 5 A battery separator was obtained in the same manner as in Example 1 except that the internal cooling water temperature of the cooling roll was kept at 0 ° C. and the doctor blade was not used.
- Comparative Example 6 Instead of cooling the polyethylene resin solution extruded from the die with a cooling roll, a battery separator was obtained in the same manner as in Example 1 except that the polyethylene resin solution was immersed in water kept at 25 ° C. for 1 minute.
- Comparative Example 7 A battery separator was obtained in the same manner as in Example 1 except that the internal cooling water temperature of the cooling roll was kept at 50 ° C.
- a polyamide-imide resin solution, alumina particles having an average particle size of 0.5 ⁇ m, and N-methyl-2-pyrrolidone were blended in a weight ratio of 26:34:40, respectively, and zirconium oxide beads (“Traceram” manufactured by Toray Industries, Inc. (registered) (Trademark) beads, 0.5 mm in diameter) were placed in a polypropylene container and dispersed for 6 hours with a paint shaker (Toyo Seiki Seisakusho). Subsequently, it filtered with the filter of 5 micrometers of filtration limits, and obtained the coating liquid (h). The coating liquid (h) was applied to the laminated polyethylene microporous membrane obtained in the same manner as in Example 1 by the gravure coating method in the same manner as in Example 1 to obtain a battery separator.
- zirconium oxide beads (“Traceram” manufactured by Toray Industries, Inc. (registered) (Trademark) beads, 0.5 mm in diameter) were placed in a polypropylene
- Table 1 shows the production conditions of Examples 1 to 14 and Comparative Examples 1 to 8.
- Table 2 shows the characteristics of the obtained laminated polyolefin microporous membrane and battery separator.
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Abstract
Description
図1に、引張試験機(図示しない)によって引っ張った状態の積層ポリオレフィン微多孔質膜と改質多孔層との積層試料の側面の様子を模式的に示している。1が積層試料、2が積層ポリオレフィン微多孔質膜、3が改質多孔層、4が両面粘着テープ、5及び5’がアルミニウム板であり、図中の矢印が引張方向である。大きさ50mm×25mm、厚さ0.5mmのアルミニウム板(5)に同じ大きさの両面粘着テープ(4)を貼り付け、その上に幅50mm×長さ100mmに切り出した試料(1)の積層ポリオレフィン微多孔質膜(2)の面を前記アルミニウム板(5)の25mm長さの片辺の端から40mmが重なるように貼り付け、はみ出た部分を切り取る。次いで、長さ100mm、幅15mm、厚さ0.5mmのアルミニウム板(5’)の片面に両面粘着テープを貼り付け、前記アルミニウム板(5)の25mm長さの試料側の片辺の端から20mmが重なるように貼り付ける。その後、アルミニウム板(5)とアルミニウム板(5’)を平行に反対方向に引張試験機を用いて、引張速度10mm/minで引っ張り、改質多孔層が剥離したときの強度を測定する。本評価方法で剥離強度が130N/15mm以上であれば、積層ポリオレフィン微多孔質膜の厚さが例えば10μm以下のような場合であっても、積層された改質多孔層が搬送中、あるいは加工中に剥がれ現象はほとんど生じない。
剥離強度の測定法として従来から用いられているT型剥離強度または180°での剥離強度は、塗布層を電池用セパレータの表面に対して垂直または垂直から斜め後方に引きはがす時の剥離力である。本評価方法によれば、これら従来の評価方法に比べてスリット工程や電池組み立て工程における擦れ耐性をより実際に即して評価することができる。
すなわち、
積層ポリオレフィン微多孔質膜とその少なくとも一方の表面に存在する改質多孔層とを有する電池用セパレータであって、前記積層ポリオレフィン微多孔質膜は、少なくともA層とB層を含んでなる多孔質積層体であり、メルトダウン温度が165℃以上であり、透気抵抗度が300sec/100ccAir以下であり、少なくとも一方の外界に面した表面に3個/cm2以上、200個/cm2以下のポリオレフィンからなる突起が不規則に存在し、前記突起は0.5μm≦H(Hは突起の高さ)および5μm≦W≦50μm(Wは突起の大きさ)をみたし、前記改質多孔層は前記積層ポリオレフィン微多孔質膜の突起を有する面上に積層され、かつ、引っ張り強度が5N/mm2以上のバインダーと無機粒子とを含む電池用セパレータである。
ここで、外界に面した表面とは、積層ポリオレフィン微多孔質膜を構成する各層の表面のうち少なくとも一方の表面は他の層の表面と接する側(界面側)に面するが、界面側に面しないもう一方の表面のことをいう。
本発明の電池用セパレータは積層ポリオレフィン微多孔質膜がA層/B層/A層、または、B層/A層/B層の3層構造が好ましく、B層に融解熱量が90J/g以上であるポリプロピレンを含んでなることがより好ましい。
本発明の電池用セパレータはB層の厚みが3μm以上、15μm以下であることが好ましい。
本発明の電池用セパレータはバインダーがポリビニルアルコール又はアクリル系樹脂を含むことが好ましい。
本発明の電池用セパレータは無機粒子が炭酸カルシウム、アルミナ、チタニア、硫酸バリウム及びベーマイトからなる群から選ばれる少なくとも1種を含むことが好ましい。
上記課題を解決するために本発明の電池用セパレータの製造方法は以下の構成を有する。すなわち、
(a)A層を構成するポリオレフィン樹脂に成形用溶剤を添加した後、溶融混練し、ポリオレフィン樹脂溶液Aを調製する工程
(b)B層を構成するポリエチレン樹脂とポリプロピレン樹脂を含むポリオレフィン樹脂に成形用溶剤を添加した後、溶融混練し、ポリオレフィン樹脂溶液Bを調製する工程
(c)工程(a)及び(b)にて得られたポリオレフィン樹脂溶液A及びBをダイより押し出して、うち少なくとも一方を、成形用溶剤除去手段により成形用溶剤が除去した表面を有する冷却ロールにて冷却し、積層ゲル状成形物を形成する工程
(d)前記積層ゲル状成形物を機械方向および幅方向に延伸し、積層延伸成形物を得る工程
(e)前記積層成形用溶剤を積層延伸成形物から前記成形用溶剤を抽出除去し、乾燥し、積層多孔質成形物を得る工程
(f)積層多孔質成形物を熱処理し、積層ポリオレフィン微多孔質膜を得る工程
(g)前記冷却ロールが接していた積層ポリオレフィン微多孔質膜の表面に、引っ張り強度が5N/mm2以上のバインダー、無機粒子及びバインダーを溶解または分散しうる溶媒とを含む塗布液を用いて積層膜を形成し、乾燥する工程。
本発明の電池用セパレータの製造方法は、前記(c)工程における成形用溶剤の除去手段がドクターブレードを用いて掻き落とす手段であることが好ましい。
本発明に用いる積層ポリオレフィン微多孔質膜の厚さの上限値は25μmが好ましく、より好ましくは20μm、さらに好ましくは16μmである。下限値は7μmが好ましく、より好ましくは9μmである。積層ポリオレフィン微多孔質膜の厚さが上記好ましい範囲であると、実用的な膜強度と孔閉塞機能を保有させることが出来き、電池ケースの単位容積当たりの面積が制約されず、今後、進むであろう電池の高容量化に適する。
[1]第一の層(A層)におけるポリオレフィン樹脂
本発明のA層を構成するポリオレフィン微多孔膜はポリエチレンを主成分とする。透過性と突刺強度を向上させる為には、ポリエチレンの含有量はポリオレフィン樹脂全体を100質量%として、80質量%以上であるのが好ましく、より好ましくは90質量%以上、さらに好ましくは100質量%である。
本発明のB層はポリオレフィンを主成分とする微多孔質膜である。B層は強度の観点から高密度ポリエチレンを50質量%以上含むことが好ましい。また、高密度ポリエチレンの重量平均分子量(以下、Mwという)は1×105以上が好ましく、より好ましくは2×105以上である。Mwの上限値はMwが8×105が好ましく、より好ましくはMwが7×105である。Mwが上記範囲であれば、製膜の安定性と最終的に得られる突刺強度とを両立することができる。
積層ポリオレフィン微多孔質膜は、上記の各種特徴を満足する範囲内ならば、目的に応じた製造方法を自由に選択することができる。微多孔質膜の製造方法としては、発泡法、相分離法、溶解再結晶法、延伸開孔法、粉末焼結法などがあり、これらの中では微細孔の均一化、コストの点で相分離法が好ましい。
本発明の積層ポリオレフィン微多孔質膜の製造方法は以下の(a)~(f)の工程を含むものである。
(a)A層を構成するポリオレフィン樹脂組成物に成形用溶剤を添加した後、溶融混練し、ポリオレフィン樹脂溶液Aを調製する工程
(b)B層を構成するポリエチレン樹脂とポリプロピレン樹脂を含むポリオレフィン樹脂組成物に成形用溶剤を添加した後、溶融混練し、ポリオレフィン樹脂溶液Bを調製する工程
(c)工程(a)及び(b)にて得られたポリオレフィン樹脂溶液A及びBをダイより押し出して、うち少なくとも一方を、成形用溶剤の除去手段により成形用溶剤を除去した表面を有する冷却ロールにて冷却し、積層ゲル状成形物を形成する工程
(d)積層ゲル状成形物を機械方向および幅方向に延伸し、積層延伸成形物を得る工程
(e)積層延伸成形物から成形用溶剤を抽出除去し、乾燥し、積層多孔質成形物を得る工程
(f)積層多孔質成形物を熱処理し、積層ポリオレフィン微多孔質膜を得る工程
さらに、工程(a)の前、工程(a)~(f)の途中、または工程(f)の後に親水化処理、除電処理等の他の工程を追加することもできる。また、工程(f)の後に、再延伸工程を設けることもできる。
(a)、(b)A層及びB層を構成するポリオレフィン樹脂に成形用溶剤を添加した後、溶融混練し、ポリオレフィン樹脂溶液A及びBを調製する工程
成形用溶剤としては、ポリオレフィンを十分に溶解できるものであれば特に限定されない。例えば、ノナン、デカン、ウンデカン、ドデカン、流動パラフィンなどの脂肪族または環式の炭化水素、あるいは沸点がこれらに対応する鉱油留分などがあげられるが、溶剤含有量が安定なゲル状成形物を得るためには流動パラフィンのような不揮発性の溶剤が好ましい。加熱溶解は、ポリオレフィン組成物が完全に溶解する温度で攪拌または押出機中で均一混合して溶解する方法で行う。その温度は、押出機中又は溶媒中で攪拌しながら溶解する場合は使用する重合体及び溶媒により異なるが、例えば140~250℃の範囲が好ましい。
押出機で溶融混練したポリオレフィン樹脂溶液AおよびBを直接に、あるいはさらに別の押出機を介して、ダイから押し立し、冷却ロールにて冷却し、積層ゲル状成形物を形成する。積層ゲル状成形物を得る方法としては、積層するゲル状成形物を別々に作製した後、カレンダーロール等を通して貼り合わせる方法(貼りあわせ法)や、ポリオレフィン溶液を別々に押出機に供給して所望の温度で溶融させ、ポリマー管あるいはダイ内で合流させて共押出して積層させ、その後に積層ゲル状成形物とする方法(共押出法)などのどの方法を使用しても良いが、層間の密着性の観点からは、共押出法を用いることが好ましい。
積層ゲル状成形物を延伸し、延伸成形物とする。延伸は、ゲル状成形物を加熱し、通常のテンター法、ロール法、もしくはこれらの方法の組み合わせによってMD及びTDの二方向に所定の倍率で行う。延伸はMD及びTD(機械方向と幅方向)の同時延伸(同時2軸延伸)または逐次延伸のいずれでもよい。逐次延伸はMDとTDの順序は問わず、MD及びTDの少なくとも一方を多段で延伸してもよい。また延伸倍率は、原反の厚さによって異なるが面倍率で9倍以上が好ましく、より好ましくは16~400倍である。MD及びTDの同時延伸であれば3×3、5×5、又は7×7などのMD及びTD同倍率での延伸が好ましい。面倍率が上記好ましい範囲であると、延伸が十分であり高弾性、高強度の微多孔質膜が得られる。また、延伸温度を調整することによって所望の透気抵抗度を得ることができる。
延伸された延伸成形物を洗浄溶剤で処理して残留する成形用溶剤を除去し、微多孔質膜を得る。洗浄溶剤としては、ペンタン、ヘキサン、ヘプタンなどの炭化水素、塩化メチレン、四塩化炭素などの塩素化炭化水素、三フッ化エタンなどのフッ化炭化水素、ジエチルエーテル、ジオキサンなどのエーテル類などの易揮発性のものを用いることができる。これらの洗浄溶剤はポリオレフィンの溶解に用いた成形用溶剤に応じて適宜選択し、単独もしくは混合して用いる。洗浄方法は、洗浄溶剤に浸漬し抽出する方法、洗浄溶剤をシャワーする方法、洗浄溶剤を延伸成形物の反対側から吸引する方法、またはこれらの組合せによる方法などにより行うことができる。上述のような洗浄は、延伸成形物である延伸成形物中の残留溶剤が1質量%未満になるまで行う。その後、洗浄溶剤を乾燥するが、洗浄溶剤の乾燥方法は加熱乾燥、風乾などの方法で行うことができる。
乾燥して得られた積層多孔質成形物を熱処理し、積層ポリオレフィン微多孔質膜を得る。熱処理温度は90~150℃にて行うのが好ましい。熱処理温度が上記好ましい範囲であると、得られた積層ポリオレフィン微多孔質膜の熱収縮率を低減し、透気抵抗度を確保することができる。熱処理時間は、特に限定されることはないが、通常は1秒以上10分以下が好ましく、より好ましくは3秒から2分以下で行われる。熱処理は、テンター方式、ロール方式、圧延方式、フリー方式のいずれも採用できる。
改質多孔層は積層ポリオレフィン微多孔質膜の突起を有する面側に積層するのが好ましい形態である。積層ポリオレフィン微多孔質膜の両面に改質多孔層を設ける場合は、スリット工程や搬送工程などの後工程において、ロールやバーなどの接触によって平行な応力がより強くかかる側の改質多孔層を積層ポリオレフィン微多孔質膜の突起を有する面側に積層するのが、本発明による効果が発揮されるため好ましい。
(g)前記冷却ロールが接していた積層ポリオレフィン微多孔質膜の表面に、引っ張り強度が5N/mm2以上のバインダー、無機粒子及びバインダーを溶解または分散しうる溶媒とを含む塗布液を用いて積層膜を形成し、乾燥する工程。
積層ポリオレフィン微多孔質膜に改質多孔層を積層する方法は、公知の方法を用いることができる。具体的には、前記塗布液を積層ポリオレフィン微多孔質膜に所定の膜厚になるように後述する方法で塗工し、乾燥温度40~80℃、乾燥時間5秒から60秒の条件下で乾燥させる方法で得ることができる。また、バインダーが可溶でかつ水と混和する溶媒で溶解した塗布液を所定の積層ポリオレフィン微多孔質膜に後述する塗布法を用いて積層し、特定の湿度環境下に置き、バインダーと水とを混和する溶媒を相分離させ、さらに水浴(凝固浴)に投入してバインダーを凝固させる方法も用いることができる。
実施例および比較例で用いたバインダーが可溶な溶媒に十分溶解または水分散させ、JIS K 7113に規定の2号形試験片作製用のダンベル型に乾燥後の膜厚が約100μmになるように入れて25℃で自然乾燥させ、さらに25℃で8時間真空乾燥(真空度3mmHg)を行って溶媒を十分除去して得られた試料シートを引っ張り強度測定に供した。
引張試験機((株)島津製作所製 Autograph AGS-J ロードセル容量1kN)を用いて以下の条件で測定した。サンプルフィルム、測定条件は以下の通りであり、3回測定を行い、その平均値をバインダーの引っ張り強度とした。
チャック間距離:40mm
試験速度:20mm/min
測定環境:気温20℃、相対湿度60%
突起の数と大きさは免震台上に設置したコンフォーカル(共焦点)顕微鏡(レーザーテック(株)製 HD100)を用いて、光源を安定化させた後に測定した。
(手順)
(1)実施例および比較例で得られた積層ポリオレフィン微多孔質膜を製膜時に冷却ロールに接していた面に1cm×1cmの正方形の枠を極細油性ペンで描いた。
(2)上記正方形の枠を描いた面を上にしてサンプルステージに載せ、コンフォーカル顕微鏡付属の静電気密着装置を用いてサンプルステージに密着固定させた。
(3)倍率5倍の対物レンズを用いて、図3のようなポリオレフィンの球晶に由来するリング状痕をモニターに二次元画像(本装置ではREAL画面と称す)として表示させ、リング状痕の最も色の濃い部分がモニター画面のほぼ中央に位置するようにサンプルステージ位置を調整した。リング状痕が2つ連なっている場合はその接点に合わせた。突起高さ測定の対象は前記ポリオレフィンの球晶に由来するリング状痕の長径が0.2mm以上のものとした。リング状痕の長径は前記二次元画像にて長径方向にリングの両端にカーソルを合わせ、その長さを読み取った。
(4)対物レンズを20倍レンズに替え、モニター画面の中央部にフォーカスを合わせて(本装置ではモニター画面の中央部が最も明るく表示されようにする)、この高さ位置を基準高さとした(本装置ではREFSETと称す)。
(5)高さ方向の測定範囲は前記基準高さを0μmとして上下15μmに設定した。また、スキャン時間120秒、STEP移動距離0.1μm/Stepとし、三次元データを取り込んだ。
(6)三次元データ取り込み後、データ処理用画像(本装置ではZ画像と称す)を表示させ、スムージング処理を行った(スムージング条件:フィルタサイズ3x3、マトリックスタイプ SMOOTH3-0、回数1回)。また、必要に応じて水平補正画面にて水平補正を行った。
(7)データ処理用画像にて最も高い突起を通る位置(最も明るい部分)に水平方向にカーソルを置き、前記カーソルに対応した断面プロファイルを、断面プロファイル画像に表示させた。
(8)断面プロファイル画像にて垂直方向に2本のカーソルを突起の両袖の変曲点に合わせ両カーソル間の距離を突起の大きさとした。
(9)断面プロファイル画像にて水平方向に2本のカーソルを突起の頂点と突起の両袖の変曲点に合わせ(突起の両袖の変曲点の高さが異なる場合は低い方)両カーソル間の距離を突起の高さとした。
(10)前記操作を前記1cm×1cmの正方形の枠内で繰り返し、大きさ5μm以上、50μm以下、高さ0.5μm以上、3.0μm以下の突起の数を数え1cm2当たりの突起数を求め、さらにその突起の高さ平均値を求めた。
図1に、評価方法を模式的に示す。1が積層試料、2が積層ポリオレフィン微多孔質膜、3が改質多孔層、4が両面粘着テープ、5及び5'がアルミニウム板であり、図中の矢印が引張方向である。大きさ50mm×25mm、厚さ0.5mmのアルミニウム板5に同じ大きさの両面粘着テープ(ニチバン(株)製NW-K50)4を貼り付けた。その上に幅50mm×長さ100mmに切り出した試料1(電池用セパレータ)の積層ポリオレフィン微多孔質膜2の面を前記アルミニウム板5の25mm長さの片辺の端から40mmが重なるように貼り付け、はみ出た部分を切り取った。次いで、長さ100mm、幅15mm、厚さ0.5mmのアルミニウム板5'の片面に両面粘着テープを貼り付け、前記アルミニウム板5の25mm長さの試料側の片辺の端から20mmが重なるように貼り付けた。その後、試料を挟持したアルミニウム板5とアルミニウム板5'を引張試験機((株)島津製作所製 Autograph AGS‐J ロードセル容量1kN)に取り付け、アルミニウム板5とアルミニウム板5'のそれぞれを平行に反対方向に引張速度10mm/minで引っ張り、改質多孔層が剥離したときの強度を測定した。この測定を長手向に30cm以上の間隔を空けた任意の3点について行い、その平均値を改質多孔層の0°剥離強度とした。
接触式膜厚計((株)ミツトヨ製 ライトマチック series318)を使用して20点の測定値を平均することによって求めた。超硬球面測定子φ9.5mmを用い、加重0.01Nの条件で測定した。
積層ポリオレフィン微多孔質膜の平均孔径は以下の方法で測定した。試料を測定用セルの上に両面テープを用いて固定し、プラチナまたは金を数分間真空蒸着させ、適度な倍率で膜の表面をSEM測定した。SEM測定で得られた画像上で任意の10箇所を選択し、それら10箇所の孔径の平均値を試料の平均孔径とした。
テスター産業(株)製のガーレー式デンソメーターB型を使用して、積層ポリオレフィン微多孔質膜又は電池用セパレータをクランピングプレートとアダプタープレートの間にシワが入らないように固定し、JIS P8117に従って測定した。試料は10cm角とし、測定点は試料の中央部と4隅の計5点として、その平均値を透気抵抗度として用いた。なお、試料の1辺の長さが10cmに満たない場合は5cm間隔で5点測定した値を用いてもよい。
透気抵抗度の上昇幅は下記の式より求めた。
透気抵抗度の上昇幅=(Y)-(X)sec/100ccAir
積層ポリオレフィン微多孔質膜の透気抵抗度(X)sec/100ccAir
電池用セパレータの透気抵抗度(Y)sec/100ccAir
熱機械的分析装置(セイコー電子工業株式会社製、TMA/SS6000)を用い、10mm(TD)×3mm(MD)の試験片を、一定の荷重2gfで試験片の長手方向に引っ張りながら、5℃/minの速度で室温から昇温し、溶融により破膜した温度をメルトダウン温度とした。
約5mgの試料を予め精秤したアルミニウム製サンプルパンに入れ、次いで試料を入れたサンプルパンの質量を精秤して、サンプルパン質量との差を試料質量とした。試料を入れたサンプルパンを走査型示差熱量計(PerkinElmer,Inc.製、DSC-System7型)の試料ホルダー内に静置し、窒素雰囲気下において40℃から190℃まで10℃/minで加熱した後、190℃/10分間の熱処理を行った。続いて、40℃まで10℃/minで冷却し、40℃で2分間保持した後、10℃/minの昇温速度で190℃まで昇温した。昇温過程で得られたDSC曲線(溶融曲線)について、85~175℃の範囲に直線ベースラインを設定し、直線ベースラインとDSC曲線とで囲まれる部分の面積から熱量を算出し、これを試料質量当りに換算した。
10cm角の試料を用意し、その試料体積(cm3)と質量(g)を測定し得られた結果から次式を用いて空孔率(%)を計算した。
空孔率=(1-質量/(樹脂密度×試料体積))×100
実施例及び比較例で得られたロール状の電池用セパレータを巻きだしながら、両端をスリット加工した。スリット加工はスリッター((株)西村製作所製 WA177A型)を用いて速度20m/分、張力60N/100mmの条件で行った。加工中、塗工面に接触するロールはハードクロムメッキロール2本(いずれもフリーロール)とした。次いで、スリット加工済のロール状電池用セパレータを巻き戻しながら目視、および拡大率10倍のスケール付きルーペ(PEAK社SCALELUPE×10)を用いて、長径0.5mm以上の改質多孔層の剥離欠点を数え、以下の判定基準で評価した。評価面積は幅100mm×長さ500mとした。(幅が100mmに満たない場合は長さを調整し、同様の評価面積になるようにした。)
判定基準
○(極めて良好):5ヶ以下
△(良好):6~15ヶ
×(不良):16ヶ以上
MwおよびMw/Mnは以下の条件でゲルパーミエーションクロマトグラフィー(GPC)法により求めた。
・測定装置:Waters Corporation製GPC-150C
・カラム:昭和電工(株)製“Shodex”(登録商標) UT806M
・カラム温度:135℃
・溶媒(移動相):o-ジクロルベンゼン
・溶媒流速:1.0ml/分
・試料濃度:0.1質量%(溶解条件:135℃/1h)
・インジェクション量:500μl
・検出器:Waters Corporation製ディファレンシャルリフラクトメーター
・検量線:単分散ポリスチレン標準試料を用いて得られた検量線から、所定の換算定数を用いて作製した。
エスアイアイ・ナノテクノロジー株式会社製の示差走査熱量計(DSC)DSC6220を用い、窒素ガス雰囲気下で樹脂試料5mgを昇温速度20℃/分で昇温したとき観察される融解ピークの頂点温度を融点とした。
重量平均分子量が200万の超高分子量ポリエチレン(UHMWPE)30重量%及び重量平均分子量が35万の高密度ポリエチレン(HDPE)70重量%からなる組成物100重量部に、酸化防止剤としてテトラキス[メチレン‐3‐(3,5‐ジターシャリーブチル‐4‐ヒドロキシフェニル)‐プロピオネート]メタン0.375重量部を加えたポリエチレン組成物Aを得た。このポリエチレン組成物A30重量部を二軸押出機に投入した。この二軸押出機のサイドフィーダーから流動パラフィン70重量部を供給し、溶融混練して、押出機中にてポリオレフィン樹脂溶液Aを調製した。
前記積層ポリエチレン微多孔質膜の、製膜時に冷却ロールに接していた面に塗布液(a)をグラビアコート法にて塗布し、50℃の熱風乾燥炉を10秒間通過させることで乾燥して、最終厚み22μmの電池用セパレータを得た。
2枚のポリエステル製ドクターブレードを20mmの間隔で冷却ロールにあてた以外は実施例1と同様にして電池用セパレータを得た。
3枚のポリエステル製ドクターブレードをそれぞれ20mmの間隔で冷却ロールにあてた以外は実施例1と同様にして電池用セパレータを得た。
水性アクリルポリオールと水分散性ポリイソシアネート(硬化剤)からなる2液硬化型水性アクリルウレタン樹脂(固形分濃度45質量%)平均粒径0.5μmのアルミナ粒子、イオン交換水をそれぞれ10:40:50の重量比率で配合し、酸化ジルコニウムビーズ(東レ(株)製“トレセラム”(登録商標)ビーズ、直径0.5mm)と共にポリプロピレン製の容器に入れ、ペイントシェーカー((株)東洋精機製作所製)で6時間分散させた。次いで、濾過限界5μmのフィルターで濾過し、塗布液(b)を得た。塗布液(a)を塗布液(b)に替えた以外は実施例1と同様に改質多孔層を積層させ、電池用セパレータを得た。
ポリビニルアルコールとアクリル酸、メタクリル酸メチルの共重合体(日新化成(株)製“POVACOATR”(登録商標))、平均粒径0.5μmのアルミナ粒子、溶媒(イオン交換水:エタノール=70:30)をそれぞれ5:45:50の重量比率で配合し、酸化ジルコニウムビーズ(東レ(株)製“トレセラム”(登録商標)ビーズ、直径0.5mm)と共にポリプロピレン製の容器に入れ、ペイントシェーカー((株)東洋精機製作所製)で6時間分散させた。濾過限界5μmのフィルターで濾過し、塗布液(c)を得た。塗布液(a)を塗布液(c)に替えた以外は実施例1と同様に改質多孔層を積層させ、電池用セパレータを得た。
冷却ロールの内部冷却水温度を35℃に保った以外は実施例2と同様にして電池用セパレータを得た。
ポリオレフィン樹脂組成物Bとして、重量平均分子量が200万の超高分子量ポリエチレン(UHMWPE)5重量%及び重量平均分子量が30万の高密度ポリエチレン(HDPE)55重量%、重量平均分子量が53万で、融解熱が96J/gのポリプロピレン40重量%からなる組成物100重量部に、酸化防止剤0.375重量部を加えた組成物を使用し、ポリエチレン組成物B30重量部に対して流動パラフィン70重量部を供給してポリオレフィン樹脂溶液Bを得た以外は実施例1と同様にして、電池用セパレータを得た。
ポリオレフィン樹脂組成物Aとして、重量平均分子量が200万の超高分子量ポリエチレン(UHMWPE)20重量%及び重量平均分子量が30万の高密度ポリエチレン(HDPE)80重量%からなる組成物100重量部に、酸化防止剤0.375重量部を加えた組成物を使用し、ポリエチレン組成物B30重量部に対して流動パラフィン70重量部を供給してポリオレフィン樹脂溶液Bを得た以外は実施例1と同様にして、電池用セパレータを得た。
ポリオレフィン製積層多孔質膜の厚みが表に記載のとおりになるようにポリオレフィン溶液AおよびBの押し出し量を調整した以外は実施例3と同様にして、電池用セパレータを得た。
ポリオレフィン組成物Aの超高分子量ポリエチレンと高密度ポリエチレンの配合比、また、ポリオレフィン組成物Bに超高分子量ポリエチレンを使用せず、高密度ポリエチレンとポリプロピレンの配合比を表のとおりとした以外は実施例1と同様にして電池用セパレータを得た。
アルミナ粒子を架橋高分子粒子(ポリメタクリル酸メチル系架橋物粒子(“エポスター”(登録商標)MA1002、(株)日本触媒製、平均粒子径2.5μm))に替え、架橋高分子粒子、N-メチル-2-ピロリドンの配合比率をそれぞれ35:10:55(重量比率)としてワニス(d)を得た。ワニス(d)を用いた以外は実施例1と同様にして電池用セパレータを得た。
フッ素系樹脂溶液(呉羽化学工業(株)製“KFポリマー”(登録商標)#9300(ポリフッ化ビニリデン(5%N-メチルピロリドン溶液)及び平均粒径0.5μmのアルミナ粒子、N-メチル-2-ピロリドンをそれぞれ16:34:50の重量比率で配合し、酸化ジルコニウムビーズ(東レ(株)製“トレセラム”(登録商標)ビーズ、直径0.5mm)と共に、ポリプロピレン製の容器に入れ、ペイントシェーカー((株)東洋精機製作所製)で6時間分散させた。次いで、濾過限界5μmのフィルターで濾過し、ワニス(e)を得た。ワニス(e)を用いた以外は実施例1と同様にして、電池用セパレータを得た。
アクリルエマルジョン(昭和電工(株)製“ポリゾール”(登録商標)AT‐731、不揮発分47%)、平均粒径0.5μmのアルミナ粒子、イオン交換水をそれぞれ2:55:43の重量比率で配合し、酸化ジルコニウムビーズ(東レ(株)製“トレセラム”(登録商標)ビーズ、直径0.5mm)と共にポリプロピレン製の容器に入れ、ペイントシェーカー((株)東洋精機製作所製)で12時間分散させた。次いで、濾過限界5μmのフィルターで濾過し、塗布液(f)を得た。塗布液(f)を、実施例1の積層ポリエチレン微多孔質膜に実施例1と同様に塗布し、電池用セパレータを得た。
アルミナ粒子を硫酸バリウム微粒子(平均粒子径0.3μm)替えた塗布液(g)を用いた以外は実施例1と同様にして、電池用セパレータを得た。
ポリエチレン溶液Aのみを用いて、190℃で単層ダイから押し出しして単層ゲル状成形物を成形し、積層ゲル状成形物の代わりに得られた単層ゲル状成形物を使用した以外は実施例1と同様にして電池用セパレータを得た。
ポリオレフィン溶液Bに用いるポリプロピレンとして、重量平均分子量が49万で、融解熱が70J/gのポリプロピレンを用いた以外は実施例8と同様にして電池用セパレータを得た。
ポリオレフィン樹脂組成物AおよびBとして、配合比、添加量、樹脂濃度を表のとおりとした以外は実施例1と同様にして電池用セパレータを得た。
ダイから押し出されたポリエチレン樹脂溶液を冷却ロールで冷却し、ゲル状成形物を得る際にドクターブレードを用いず、冷却ロール上に付着している流動パラフィンを掻き落とさなかった以外は実施例1と同様にして、電池用セパレータを得た。
冷却ロールの内部冷却水温度を0℃に保ち、ドクターブレードを用いなかった以外は実施例1と同様にして、電池用セパレータを得た。
ダイから押し出されたポリエチレン樹脂溶液を冷却ロールで冷却する替わりに、25℃に保った水中に1分間浸漬した以外は実施例1と同様にして、電池用セパレータを得た。
冷却ロールの内部冷却水温度を50℃に保った以外は実施例1と同様にして、電池用セパレータを得た。
温度計、冷却管、窒素ガス導入管のついた4ツ口フラスコにトリメリット酸無水物(TMA)1モル、o-トリジンジイソシアネート(TODI)0.8モル、2,4-トリレンジイソシアネート(TDI)0.2モル、フッ化カリウム0.01モルを固形分濃度が14%となるようにN-メチル-2-ピロリドンと共に仕込み、100℃で5時間攪拌した後、固形分濃度が14%となるようにN-メチル-2-ピロリドンで希釈してポリアミドイミド樹脂溶液を合成した。
ポリアミドイミド樹脂溶液及び平均粒径0.5μmのアルミナ粒子、N-メチル-2-ピロリドンをそれぞれ26:34:40の重量比率で配合し、酸化ジルコニウムビーズ(東レ(株)製“トレセラム”(登録商標)ビーズ、直径0.5mm)と共にポリプロピレン製の容器に入れ、ペイントシェーカー((株)東洋精機製作所製)で6時間分散させた。次いで、濾過限界5μmのフィルターで濾過し、塗布液(h)を得た。塗布液(h)を実施例1と同様にして得られた積層ポリエチレン微多孔質膜にグラビアコート法にて実施例1と同様に塗布し、電池用セパレータを得た。
2 積層ポリエチレン微多孔質膜
3 改質多孔層
4 両面粘着テープ
5、5’ アルミニウム板
6 ポリエチレン球晶の結晶核
7 ダイ
8 ポリエチレン樹脂溶液
9 冷却ロール
10 ドクターブレード
11 ゲル状成形物
Claims (7)
- 積層ポリオレフィン微多孔質膜とその少なくとも一方の表面に存在する改質多孔層とを有する電池用セパレータであって、前記積層ポリオレフィン微多孔質膜は、少なくともA層とB層を含んでなる多孔質積層体であり、メルトダウン温度が165℃以上であり、透気抵抗度が300sec/100ccAir以下であり、少なくとも一方の外界に面した表面に3個/cm2以上、200個/cm2以下のポリオレフィンからなる突起が不規則に存在し、前記突起は0.5μm≦H(Hは突起の高さ)および5μm≦W≦50μm(Wは突起の大きさ)をみたし、前記改質多孔層は前記積層ポリオレフィン微多孔質膜の突起を有する面上に積層され、かつ、引っ張り強度が5N/mm2以上のバインダーと無機粒子とを含む電池用セパレータ。
- 積層ポリオレフィン微多孔質膜がA層/B層/A層、または、B層/A層/B層の3層構造であり、B層に融解熱量が90J/g以上であるポリプロピレンを含んでなることを特徴とする請求項1に記載の電池用セパレータ。
- B層の厚みが3μm以上、15μm以下である請求項1または2に記載の電池用セパレータ。
- バインダーがポリビニルアルコール又はアクリル系樹脂を含む請求項1~3のいずれか1つに記載の電池用セパレータ。
- 無機粒子が炭酸カルシウム、アルミナ、チタニア、硫酸バリウム及びベーマイトからなる群から選ばれる少なくとも1種を含む請求項1~4のいずれか1つに記載の電池用セパレータ。
- 以下の工程(a)~(g)を含む、請求項1~5のいずれか1つに記載の電池用セパレータの製造方法。
(a)A層を構成するポリオレフィン樹脂に成形用溶剤を添加した後、溶融混練し、ポリオレフィン樹脂溶液Aを調製する工程
(b)B層を構成するポリエチレン樹脂とポリプロピレン樹脂を含むポリオレフィン樹脂に成形用溶剤を添加した後、溶融混練し、ポリオレフィン樹脂溶液Bを調製する工程
(c)工程(a)及び(b)にて得られたポリオレフィン樹脂溶液A及びBをダイより押し出して、うち少なくとも一方を、成形用溶剤除去手段により成形用溶剤が除去した表面を有する冷却ロールにて冷却し、積層ゲル状成形物を形成する工程
(d)前記積層ゲル状成形物を機械方向および幅方向に延伸し、積層延伸成形物を得る工程
(e)前記積層成形用溶剤を積層延伸成形物から前記成形用溶剤を抽出除去し、乾燥し、積層多孔質成形物を得る工程
(f)積層多孔質成形物を熱処理し、積層ポリオレフィン微多孔質膜を得る工程
(g)前記冷却ロールが接していた積層ポリオレフィン微多孔質膜の表面に、引っ張り強度が5N/mm2以上のバインダー、無機粒子及びバインダーを溶解または分散しうる溶媒とを含む塗布液を用いて積層膜を形成し、乾燥する工程。 - 前記(c)工程における成形用溶剤除去手段がドクターブレードを用いて掻き落とす手段である請求項6に記載の電池用セパレータの製造方法。
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CN106415885B (zh) | 2019-02-19 |
JP5876629B1 (ja) | 2016-03-02 |
JPWO2015190265A1 (ja) | 2017-04-20 |
KR20170019345A (ko) | 2017-02-21 |
KR102316033B1 (ko) | 2021-10-21 |
CN106415885A (zh) | 2017-02-15 |
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